life processes

Life processes

Living organisms have certain life processes in common. There are seven things that they need to do to count as being alive. The phrase MRS GREN is one way to remember them:

  • Movement - all living things move, even plants

  • Respiration - getting energy from food

  • Sensitivity - detecting changes in the surroundings

  • Growth - all living things grow

  • Reproduction - making more living things of the same type

  • Excretion - getting rid of waste

  • Nutrition - taking in and using food

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life processes

It can be easy to tell if something is living or not. A teddy bear might look like a bear, but it cannot do any of the seven things it needs to be able to do to count as being alive.

A car can move, it gets energy from petrol (like nutrition and respiration), it might have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust pipe (excretion). But it cannot grow or make baby cars. So a car is not alive.

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organisms are made up of cells .

Animal and plant cells both have a cell membrane, cytoplasm, and a nucleus. Plant cells also have chloroplasts, a vacuole and a cell wall (

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Animal cells and plant cells both contain:

Plant cells also contain these parts, which are not found in animal cells:

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Cells and their functions

Humans are multicellular. That means we are made of lots of cells, not just one cell. The cells in many multicellular animals and plants arespecialised, so that they can share out the processes of life. They work together like a team to support the different processes in an organism.

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Cells, tissues, organs and systems

Cells, tissues, organs and systems

Multicellular organisms are organised into increasingly complex parts. In order, from least complex to most complex:

  • cells

  • tissues

  • organs

  • organ systems

  • organism

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Cells, tissues, organs and systems


Animal cells and plant cells can form tissues, such as muscle tissue in animals. A living tissue is made from a group of cells with a similar structure and function, which all work together to do a particular job. Here are some examples of tissues:

  • muscle

  • the lining of the intestine

  • the lining of the lungs

  • xylem (tubes that carry water in a plant)

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Cells, tissues, organs and systems

Organ systems

An organ system is made from a group of different organs, which all work together to do a particular job. Here are some examples of organ systems:

  • circulatory system

  • respiratory system

  • digestive system

  • nervous system

  • reproductive system

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the skeleton

The skeleton

Our skeleton is made of more than 200 bones. Calcium and other minerals make the bone strong but slightly flexible. Bone is a livingtissue with a blood supply. It is constantly being dissolved and formed, and it can repair itself if a bone is broken.

Function of the skeleton

The skeleton has four main functions:

  • to support the body
  • to protect some of the vital organs of the body
  • to help the body move
  • to make blood cells
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the skeleton

Human skeleton, with the bones labelled: skull, clavicle, sternum, rib cage, spine, humerus, radius, ulna, femur, tibia and fibula. (

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Bones are linked together by joints. Most joints allow different parts of the skeleton to move. The human skeleton has joints called synovial joints.

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The synovial joint

The synovial joint

If two bones just moved against each other, they would eventually wear away. This can happen in people who have a condition called arthritis. To stop this happening, the ends of the bones in a joint are covered with a tough, smooth substance called cartilage. This is kept slippery by a liquid called synovial fluid. Tough ligaments join the two bones in the joint and stop the joint falling apart.

Synovial joint: featuring bone, cartilage, ligament, synovial fluid and synovial membrane. (

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Muscles work by getting shorter. We say that theycontract, and the process is called contraction. Muscles are attached to bones by strong tendons. When a muscle contracts, it pulls on the bone, and the bone can move if it is part of a joint.

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Antagonistic muscles

Antagonistic muscles

Muscles can only pull and cannot push. This would be a problem if a joint were controlled by just one muscle. As soon as the muscle had contracted and pulled on a bone, that would be it, with no way to move the bone back again. This problem is solved by having muscles in pairs, calledantagonistic muscles.

For example, your elbow joint has two muscles that move your forearm up or down. These are the biceps on the front of the upper arm and the triceps on the back of the upper arm:

  • to raise the forearm, the biceps contracts and the triceps relaxes
  • to lower the forearm again, the triceps contracts and the biceps relaxes
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